The CORE will provide expertise int he derivation of retroviral producer clones and, in the standardized preparation of such vectors for use in cell culture and animal model experimentation. The CORE will also be responsible for preparing recombinant adeno-associated (rAAV) viral vectors as needed using standardized methods. All vector preparations will be characterized with respect to the concentration of vector particles. Retroviral vector preparations will be assayed using the RNA slot blot to estimate physical particle numbers as reflected by RNA content of a standard aliquot. In addition, these vector preparations will be characterized with respect to gene transfer into target cell populations including selection for dominant resistant markers, when present, or by determination of the concentration of the proviral genome in test cells infected under standardized conditions. The physical particle number of rAAV will be assayed by determining the amount of DNAse protected vector genomic DNA in a standard aliquot of the preparation. The infectivity titer will be estimated by determining the level of transient expression using immunological methodology as appropriate by detecting the expressed mRNA in target cells. The transducing titer will be determined by evaluating stable integration into a standard, test cell target. The use of standard methods of preparation and assay will ensure that investigators in each of the projects that depend on the CORE will be provided with vector preparations suitable for their experimental applications.